CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-PAS-TOP-21-014
Measurement of the $\mathrm{t\bar{t}}$ charge asymmetry in highly boosted events in the single-lepton channel at 13 TeV
Abstract: The measurement of the charge asymmetry for highly boosted top quark pairs decaying to a single lepton and jets is presented. The analysis is performed using 138 fb$^{-1}$ of data collected in pp collisions at $\sqrt{s}= $ 13 TeV with the CMS detector during Run 2 of the Large Hadron Collider. The selection is optimized for top quark-antiquark pairs produced with large Lorentz boosts, resulting in non-isolated leptons and overlapping jets. The top quark charge asymmetry is measured for events with $\mathrm{t\bar{t}}$ invariant mass larger than 750 GeV and corrected for detector and acceptance effects using a binned maximum likelihood fit. The measured top quark charge asymmetry is in good agreement with the standard model prediction at next-to-next-to-leading order in perturbation theory with next-to-leading order electroweak corrections. Differential distributions for two invariant mass ranges are also presented.
Figures & Tables Summary References CMS Publications
Figures

png pdf
Figure 1:
Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$+jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta |y|$ (top left), reconstructed $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} $ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.

png pdf
Figure 1-a:
Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$+jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta |y|$ (top left), reconstructed $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} $ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.

png pdf
Figure 1-b:
Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$+jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta |y|$ (top left), reconstructed $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} $ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.

png pdf
Figure 1-c:
Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$+jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta |y|$ (top left), reconstructed $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} $ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.

png pdf
Figure 1-d:
Comparison between data and SM prediction for the events in the signal candidate sample in the combined $\ell$+jets channel after the likelihood normalization (see Section 6) for several quantities: $\Delta |y|$ (top left), reconstructed $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} $ (top right), distance between the lepton and the closest AK4 jet ${\Delta R_{\text {min}}(\ell, j)}$ (bottom left), and the number of AK4 jets (bottom right). Data points are shown with their statistical uncertainty. The shaded band combines the MC statistical uncertainty and the systematic uncertainty (see Section 5). Overall, good agreement between data and simulation is observed in all variables.

png pdf
Figure 2:
Comparison between data and SM prediction for ${\Delta |y|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $ \le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le $ 900 GeV, and the plots in the bottom row to $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} > $ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.

png pdf
Figure 2-a:
Comparison between data and SM prediction for ${\Delta |y|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $ \le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le $ 900 GeV, and the plots in the bottom row to $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} > $ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.

png pdf
Figure 2-b:
Comparison between data and SM prediction for ${\Delta |y|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $ \le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le $ 900 GeV, and the plots in the bottom row to $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} > $ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.

png pdf
Figure 2-c:
Comparison between data and SM prediction for ${\Delta |y|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $ \le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le $ 900 GeV, and the plots in the bottom row to $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} > $ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.

png pdf
Figure 2-d:
Comparison between data and SM prediction for ${\Delta |y|}$ for each of the 12 analysis channels both before (left) and after (right) the likelihood normalization. The plots in the top row correspond to 750 GeV $ \le {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \le $ 900 GeV, and the plots in the bottom row to $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} > $ 900 GeV. Data points are shown with statistical uncertainty, and the shaded band combines the MC statistical uncertainty and the systematic uncertainty. As can be observed, these uncertainties are reduced significantly after the likelihood fit, and the agreement between data and simulation is improved. Overall, excellent agreement in all channels is observed.

png pdf
Figure 3:
The measured ${A_{C}}$ values in different mass regions, combining the $ \mu$+jets and e+jets channels, compared with the prediction in the fiducial region obtained by fitting Asimov data (left) and the theoretical prediction including NNLO QCD and NLO EW corrections from Ref. [4] (right).

png pdf
Figure 3-a:
The measured ${A_{C}}$ values in different mass regions, combining the $ \mu$+jets and e+jets channels, compared with the prediction in the fiducial region obtained by fitting Asimov data (left) and the theoretical prediction including NNLO QCD and NLO EW corrections from Ref. [4] (right).

png pdf
Figure 3-b:
The measured ${A_{C}}$ values in different mass regions, combining the $ \mu$+jets and e+jets channels, compared with the prediction in the fiducial region obtained by fitting Asimov data (left) and the theoretical prediction including NNLO QCD and NLO EW corrections from Ref. [4] (right).

png pdf
Figure 4:
The impacts of the nuisance parameters corresponding to the systematic uncertainties for the inclusive ${A_{C}}$ measurement for $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} \ge $ 750 GeV. The blue and red bars show the effect on the unfolded ${A_{C}}$ values for up and down variations of the systematic uncertainty. MC statistical uncertainties are omitted here.
Tables

png pdf
Table 1:
Event yields after the likelihood fit for each of the 12 channels used in the analysis ($ \mu$+jets, e+jets and 3 years: 2018, 2017, and 2016), separated into the two mass regions, for events that pass the signal sample selection. The errors shown include both the MC statistical and the total systematic uncertainty.

png pdf
Table 2:
Measured unfolded charge asymmetry at fiducial phase level in individual channels compared with the SM predictions.
Summary
The first measurement of the charge asymmetry for highly boosted top quark-antiquark pairs in pp collisions at $\sqrt{s} = $ 13 TeV has been presented based on 138 fb$^{-1}$ of data. The selection was optimized for top quark-antiquark pairs produced with large Lorentz boosts and decaying to a single lepton + jets, resulting in non-isolated leptons and overlapping jets. The top quark charge asymmetry is corrected for detector and acceptance effects using a binned maximum likelihood fit. The resulting unfolded charge asymmetry for $\mathrm{t\bar{t}}$ events with ${M_{\mathrm{t\bar{t}}}} \ge $ 750 GeV corrected to the full phase space is ${{A_{C}} ^{\text{full}}} = $ 0.0069$_{-0.0069}^{+0.0065}$. The corresponding theoretical prediction at NNLO in perturbation theory with NLO electroweak corrections from Ref. [4] is 0.0094$^{+0.0005}_{-0.0007}$. Good agreement between the data and the SM prediction is observed.
References
1 M. Czakon, P. Fiedler, and A. Mitov Total top-quark pair-production cross section at hadron colliders through $ o(\alpha^4_s) $ PRL 110 (2013) 252004 1303.6254
2 S. Catani et al. Top-quark pair production at the LHC: Fully differential QCD predictions at NNLO JHEP 07 (2019) 100 1906.06535
3 M. Czakon, P. Fiedler, and A. Mitov Resolving the Tevatron top quark forward-backward asymmetry puzzle: Fully differential next-to-next-to-leading-order calculation PRL 115 (2015) 052001 1411.3007
4 M. Czakon et al. Top-quark charge asymmetry at the LHC and Tevatron through NNLO QCD and NLO EW PRD 98 (2018) 014003 1711.03945
5 M. Czakon, D. Heymes, and A. Mitov High-precision differential predictions for top-quark pairs at the LHC PRL 116 (2016) 082003 1511.00549
6 J. Rojo et al. The PDF4LHC report on PDFs and LHC data: results from Run I and preparation for Run II JPG 42 (2015) 103103 1507.00556
7 J. A. Aguilar-Saavedra, A. Juste, and F. Rubbo Boosting the $ \mathrm{t\bar{t}} $ charge asymmetry PLB 707 (2012) 92 1109.3710
8 O. Antunano, J. H. Kuhn, and G. Rodrigo Top quarks, axigluons and charge asymmetries at hadron colliders PRD 77 (2008) 014003 0709.1652
9 P. H. Frampton, J. Shu, and K. Wang Axigluon as possible explanation for $ {\mathrm{p}}\mathrm{\bar{p}}\to\mathrm{t\bar{t}} $ forward--backward asymmetry PLB 683 (2010) 294 0911.2955
10 J. L. Rosner Prominent decay modes of a leptophobic $ Z^\prime $ PLB 387 (1996) 113 hep-ph/9607207
11 P. Ferrario and G. Rodrigo Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders PRD 78 (2008) 094018 0809.3354
12 P. Ferrario and G. Rodrigo Constraining heavy colored resonances from top-antitop quark events PRD 80 (2009) 051701 0906.5541
13 J. A. Aguilar-Saavedra and M. P\'erez-Victoria Asymmetries in $ t\overline{t} $ production: LHC versus Tevatron PRD 84 (2011) 115013 1105.4606
14 J. A. Aguilar-Saavedra and M. Perez-Victoria Simple models for the top asymmetry: Constraints and predictions JHEP 09 (2011) 097 1107.0841
15 C. Zhang and S. Willenbrock Effective-field-theory approach to top-quark production and decay PRD 83 (2011) 034006 1008.3869
16 T. Aaltonen et al. Evidence for a mass dependent forward-backward asymmetry in top quark pair production PRD 83 (2011) 112003 1101.0034
17 V. M. Abazov et al. Forward-backward asymmetry in top quark-antiquark production PRD 84 (2011) 112005 1107.4995
18 S. Frixione and B. R. Webber Matching NLO QCD computations and parton shower simulations JHEP 06 (2002) 029 hep-ph/0204244
19 T. Aaltonen et al. Combined forward-backward asymmetry measurements in top-antitop quark production at the Tevatron PRL 120 (2018) 042001 1709.04894
20 J. A. Aguilar-Saavedra, D. Amidei, A. Juste, and M. P\'erez-Victoria Asymmetries in top quark pair production at hadron colliders Rev. Mod. Phys. 87 (2015) 421 1406.1798
21 CMS Collaboration Search for resonant $ \mathrm{t}\overline{\mathrm{t}} $ production in proton-proton collisions at $ \sqrt{s}= $ 13 TeV JHEP 04 (2019) 031 CMS-B2G-17-017
1810.05905
22 CMS Collaboration Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s} = $ 13 TeV JINST 15 (2020) P10017 CMS-TRG-17-001
2006.10165
23 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
24 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004 CMS-00-001
25 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector JINST 12 (2017) P10003 CMS-PRF-14-001
1706.04965
26 CMS Collaboration Description and performance of track and primary-vertex reconstruction with the CMS tracker JINST 9 (2014) P10009 CMS-TRK-11-001
1405.6569
27 CMS Collaboration Technical proposal for the Phase-II upgrade of the Compact Muon Solenoid CMS-PAS-TDR-15-002 CMS-PAS-TDR-15-002
28 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm JHEP 04 (2008) 063 0802.1189
29 M. Cacciari, G. P. Salam, and G. Soyez FastJet user manual EPJC 72 (2012) 1896 1111.6097
30 CMS Collaboration Performance of missing transverse momentum reconstruction in proton-proton collisions at $ \sqrt{s} = $ 13 TeV using the CMS detector JINST 14 (2019) P07004 CMS-JME-17-001
1903.06078
31 CMS Collaboration Determination of jet energy calibration and transverse momentum resolution in CMS JINST 6 (2011) P11002 CMS-JME-10-011
1107.4277
32 A. J. Larkoski, S. Marzani, G. Soyez, and J. Thaler Soft Drop JHEP 05 (2014) 146 1402.2657
33 J. Thaler and K. Van Tilburg Identifying boosted objects with N-subjettiness JHEP 03 (2011) 015 1011.2268
34 E. Bols et al. Jet flavour classification using DeepJet JINST 15 (2020), no. 12, P12012 2008.10519
35 CMS Collaboration Precision luminosity measurement in proton-proton collisions at $ \sqrt{s} = $ 13 TeV in 2015 and 2016 at CMS EPJC 81 (2021) 800 CMS-LUM-17-003
2104.01927
36 CMS Collaboration CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s} = $ 13 TeV CMS-PAS-LUM-17-004 CMS-PAS-LUM-17-004
37 CMS Collaboration CMS luminosity measurement for the 2018 data-taking period at $ \sqrt{s} = $ 13 TeV CMS-PAS-LUM-18-002 CMS-PAS-LUM-18-002
38 S. Alioli, P. Nason, C. Oleari, and Re A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX JHEP 06 (2010) 043 1002.2581
39 J. Alwall et al. The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations JHEP 07 (2014) 079 1405.0301
40 T. Sjostrand et al. An introduction to PYTHIA 8.2 CPC 191 (2015) 159 1410.3012
41 CMS Collaboration Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements EPJC 80 (2020) 4 CMS-GEN-17-001
1903.12179
42 R. J. Barlow and C. Beeston Fitting using finite Monte Carlo samples CPC 77 (1993) 219
Compact Muon Solenoid
LHC, CERN